Waterborne dispersions of epoxy resins are disclosed, for example, in U.S. Pat. Nos. 5,118,729; 5,344,856; 5,424,340; 5,602,193; and 6,271,287; and Japanese Patent Application Kokai: Hei 3-157445, which disclosures are incorporated herein by reference.
One of the problems with state-of-the-art waterborne epoxy dispersions is that the shelf-stability of the dispersions is not sufficiently long enough for practical use, (i.e., the dispersions should have a shelf-life of greater than six months for practical use). The problem of shelf-stability is exacerbated when epoxy resins containing nanofillers are used. The shelf-life of epoxy resins containing nanofillers is less than six months, and the coatings produced from such dispersions have defects. It would therefore be an advantage in the art to discover a waterborne, nanofiller-containing epoxy resin which has a long (greater than 6 months) shelf-stability.
None of the above-mentioned prior art patents make reference to a waterborne epoxy dispersion containing nanofillers. Instead, the prior art patents describe solutions for the stability problem for epoxy resins which do not contain nanofillers. For example, U.S. Pat. No. 6,271,287 describes the selection of certain nonionic surfactants to produce stable epoxy dispersions. However, U.S. Pat. No. 6,271,287 does not describe: (i) the use surfactants in combination with epoxy resins containing nanofillers, (ii) the stability issues faced with the use of epoxy resins containing nanofillers, or (iii) the problems faced with the use of nanofiller-containing epoxy resins or dispersions in combination with water-soluble hardeners or emulsion curing agents for making waterborne coatings.
One route to prepare waterborne coatings is to use a liquid epoxy resin in combination with an emulsion of a curing agent, which is capable of emulsifying the liquid epoxy resin. If the liquid epoxy resin contains nanofillers like nanosilica, the coating made from such two-component epoxy system shows major defects such as the presence of particles or agglomerates in the coating. In addition, the known epoxy systems containing nanofillers have such a short potlife that consequently the resultant resins are impractical to use under standard conditions.
Some commercial epoxy resins containing nanofillers are currently available and such nanofiller-containing resins are used to improve properties to a coating made therefrom. For example, the abrasion resistance, toughness or other mechanical properties of the coating can be improved by using such commercial epoxy resins containing nanofillers. Also, the flame retardant properties of the resins containing nanofillers can be improved. However, when these known resins, which already contain nanofillers, are formulated with waterborne hardeners, like water-soluble epoxy amine adducts, the resulting coatings from such formulations either have a very short potlife, so that the coatings can not be applied to a substrate in a practical way or within a practical time period; or the resultant coatings show particles and agglomerates. These disadvantageous phenomena can not be observed with similar resins that do not contain any nanofillers.
Therefore, it is desirable to provide a dispersible resin and/or a dispersion of an epoxy resin containing a nanofiller which does not have the problems of the prior art. It is also desirable to produce dispersion resins which contain nanofillers; and to make the resins themselves usable in combination with conventional hardeners specifically developed to disperse liquid epoxy resins. It is further desired to provide waterborne coatings and glass fiber sizings made from such nanofiller-containing epoxy resin dispersions.